The present invention relates to a redundancy system switching control system for two packages constituting a redundancy system.
Conventional switching control for packages constituting a redundancy system is performed as follows. For example, as shown in FIG. 3 as a block diagram showing a conventional switching control system for packages and in FIGS. 4A and 4D showing timing charts used for explaining an operation of the system, in addition to packages 201 and 202 constituting the redundancy system, a third package constituting a switching control unit 203 is arranged. The switching control unit 203 serving as the third package collects pieces of alarm information a and c from the package 201 and 202 constituting the redundancy system (FIGS. 4A and 4C), determines, and transmits selection signals b and d serving as operating system information and standby system information to the packages 201 and 202 constituting the redundancy system, respectively, thereby performing switching control (FIGS. 4B and 4D).
In addition, for example, as shown in FIG. 5 showing another conventional switching control system for packages and in FIGS. 6A and 6E showing timing charts used for explaining an operation of the system, packages 305 and 306 comprise AND circuits 301 and 303 and NAND circuits 302 and 304 serving as logic elements, respectively, and the outputs from the NAND circuits 302 and 304 are alternately input/output. When an alarm output at logic level "0" is generated by the package 305, the output from the NAND circuit 302 goes to logic level "1" (FIG. 6D), and the package 306 is selected as an operating system package. At the same time, the output from the NAND circuit 304 goes to logic level "0" (FIG. 6C), and the package 305 serves as a standby system package. Similarly, when an alarm output is generated by the package 306, the package 305 serves as the standby system package (FIGS. 6E and 6C). In addition, when a forcible switching control input supplied to a forcible switching control terminal 311 of the package 305 serving as the operating system package is set at logic level "0", the package 306 serves as the operating system (FIGS. 6B and 6D). With the above operation, switching control is realized.
In FIG. 5, reference numerals 310 and 313 denote alarm information input terminals receiving alarm outputs; 312 and 315, selection information output terminals which can obtain selection information outputs; and 311 and 314, forcible switching control input terminals for receiving forcible switching control inputs.
In the above switching control system shown in FIG. 3, since the switching control unit 203 serving as the third package for performing switching control does not have a redundancy arrangement, when the third package fails, switching control for the redundancy system is disabled.
In addition, in the switching control system shown in FIG. 5, since forcible switching control information must be transmitted to an operating system package, when the forcible switching control information cannot be transmitted to the operating system package due to some trouble such that the trouble cannot be detected by the operating system package, forcible switching control cannot be performed. Therefore, although a standby system package is perfectly normal, switching control is disabled.